I've never had any problems with this pipe and one day it came off in flight.I always check those bolts to and I dont know what happenedAny way I lost the metal spacer and now bolt it directly to the motor,which is cool BUt no matter what I use it wont stay tignt.Double nuts,longer screws,red locktight,nothing is working.Thunder tiger dont even have a part number for it ,the spacer that is how can I get one

when you tighten the bolt to the muffler, did you use the 'L' shape allen key to torque the bolt down further.
if the muffler thread is strip, you can drill the remainder thread out with a 3mm drill bit and use a longer bolt and use a regular nut (not lock nut that has the nylon lock) to fasten. try not to use any lock washer on either end of the bolt or a muffler gasket. they just add another point of failure and will generally give away. just use bolt and nut. also apply red locktite on the thread where the nut will sit and torque the bolt with the allen key while holding the nut with a wrench, but dont torque the nut itself. let the red locktite cure for one evening.

Tam

I'm having a similiar problem however I'm having problems finding a 3mm x 35 or longer hex screw. The closest one i can find is a 3mm x 50mm, have to cut it down. Not sure I understand why to torque the bolt sid and not the nut?

Hexcrews has 3Mx 35-40- 45mm. screws.

I use the smoothie with 45mm screws that I got from Rons heliproz. I use nylock nuts and have not had a problem with it since. As for the spacer block I would say it is definately needed as it reduces the exhaust port to the header of the muffler. You may run into tuning issues by not using it. You may try contacting rocky or someone at customer service at ace and see if they can get a spacer block for you.
Hope this helps
Jason

No spacers available,they gave me a part number for a spacer for the 46 pro which has the same bolt holes

Clean the bolt shank and holes in the engine cylinder they pass through. Take some RTV and coat the bolt shank and insert into the engine to secure the muffler. The bolts will not move from engine vibration as it is cushioned and also bonded to the cylinder. You now have vibration isolation and the bolt is also locked from backing off.

Just another way to skin the cat

There may be some alternates on this site but you need the bolt spacing etc to select which spacer to use.